Many power systems have multiple generator sets for supplying electricity to power loads. Often, these generator sets are connected to supply the power in parallel via a common bus. After one generator set is connected to the common bus, any additional generator sets connected to the bus should produce power matching the voltage, frequency, and phase angle of the power produced by the first generator set. This matching is also known as electrically synchronizing the generator sets. A better sync, results in a smoother transition and a lower shock on the generator and load.
When multiple generators are located near each other, as is the case in a common power plant or onboard a large marine vessel, vibrations from the various generator sets can travel through the mountings thereof and either dampen or amplify. Vibrations within the power plant or onboard the marine vessel can be excessive when the engines of the generator sets have odd numbers of cylinders. That is, an engine having an odd number of cylinders is mechanically unbalanced. For example, in a nine-cylinder engine, four pistons may be moving upward, while five pistons are moving downward. As a result of the unbalanced masses and their movements, there will be a greater resultant force in the downward direction of this example. Dependent on the weight and speed of such an engine, the size of the pistons, and the type of mounting (rigid or flexible), this force could be significant enough to transmit vibrations into the engine mounts and surrounding supports with enough amplitude that structural damage could occur and/or that the vibrations become a nuisance for the engine owner/operator. This is also a problem when multiple engines located near each other are operated in sync with each other (i.e., when eight pistons are moving upward and ten are moving downward, as would be the case with two closely operating nine-cylinder engines).
One system addressing the issue of synchronizing multiple generator sets is described in U.S. Pat. No. 6,552,454 (the '454 patent) issued to Kern et al. on Apr. 22, 2003. The '454 patent discloses a generator structure having first and second generator sets positioned within a common enclosure. Each generator set includes an engine and an alternator driven by the engine for generating electrical power. The first generator set produces electrical power of a first magnitude and frequency, and the second generator set produces electrical power of a second magnitude and frequency. The generator structure also includes a controller that monitors the magnitude and phase of the electrical power produced by the first and second generator sets, and adjusts the speed of the engines via an electronic governor such the power produced by the first and second generators is brought into alignment with each other, no phase difference between the associated sine waves exist, and so that the sine waves are at the same frequency. In addition, the system controller regulates the output voltages of the generator sets such that the output voltages are generally equal. Once the frequency and output voltages are synchronized, the system controller closes switches to connect the power from the first and second generator sets to a load.
Although the generator structure of the '454 patent may allow phase, frequency, and voltage matching, it does little to account for vibrations caused by imbalanced engines. And, because the generator sets are close-coupled in a common enclosure, depending on when the engines are electrically synchronized, it may be possible for the two generators to be electrically synchronized when the two associated engines are in phase with each other. And, if the engines are in phase enough and imbalanced, the vibrations could be severe enough to damage the common enclosure.
The power system of the present disclosure addresses one or more of the problems set forth above.